Method and apparatus for processing video signal

ABSTRACT

A method for processing a vide signal according to the present invention comprises: determining a length of a current string, which is decoded on the basis of a sample string matching technique in a current block; determining a reference string on the basis of at least one between the length of the current string and a string vector for the current string; and predicting the current string using the reference string.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Patent Application of PCTInternational Patent Application No. PCT/KR2015/010282 (filed on Sep.30, 2015) under 35 U.S.C. § 371, which claims priority to Korean PatentApplication Nos. 10-2014-0132470 (filed on Oct. 1, 2014) and10-2014-0135514 (filed on Oct. 8, 2014), the teachings of which areincorporated herein in their entireties by reference.

TECHNICAL FIELD

The present invention relates to a method and a device for processing avideo signal.

BACKGROUND ART

Demands for high-resolution, high-quality images such as High Definition(HD) images and Ultra High Definition (UHD) images have recentlyincreased in various fields of applications. As video data has a higherresolution and higher quality, the video data is larger in amount thantraditional video data. Therefore, if video data is transmitted on anexisting medium such as a wired/wireless wideband circuit or stored inan existing storage medium, transmission cost and storage cost increase.To avert these problems encountered with higher-resolution,higher-quality video data, high-efficiency video compression techniquesmay be used.

There are a variety of video compression techniques includinginter-picture prediction in which pixel values included in a currentpicture are predicted from a picture previous to or following thecurrent picture, intra-picture prediction in which pixel values includedin a current picture are predicted using pixel information in thecurrent picture, and entropy encoding in which a short code is assignedto a more frequent value and a long code is assigned to a less frequentvalue. Video data may be compressed effectively and transmitted orstored, using such a video compression technique.

Along with the increasing demands for high-resolution videos, demandsfor three-dimensional (3D) video content as a new video service havebeen increasing. A video compression technique for effectively providingHD and UHD 3D video content is under discussion.

DISCLOSURE Technical Problem

It is an object of the present invention to provide a method andapparatus for predicting or restoring a video signal based on an indexstring matching technique in encoding/decoding a video signal.

It is an object of the present invention to provide a method andapparatus for predicting or restoring a video signal based on a samplestring matching technique in encoding/decoding a video signal.

Technical Solution

A video signal decoding method and apparatus according to the presentinvention determines, based on a sample string matching technique, alength of a current string to be decoded in a current block anddetermines a reference string based on at least one of a length of thecurrent string or a string vector relating to the current string, andpredict the current string using the determined reference string.

In the method and apparatus for decoding a video signal according to thepresent invention, the length of the current string is determined basedon the encoded string length information.

In the method and apparatus for decoding a video signal according to thepresent invention, the step of determining the length of the currentstring may include obtaining a string row flag (string_same_row_flag)for the current string from a bitstream, obtaining, based on the stringrow flag, the string last vector information for specifying the positionof the last sample of the current string from the bitstream, anddetermining a length of the current string based on the position of thefirst sample of the current string and the obtained string last vectorinformation.

In the method and apparatus for decoding a video signal according to thepresent invention, the string row flag indicates whether the firstsample and the last sample of the current string belong to the same row.

In the method and apparatus for decoding a video signal according to thepresent invention, the string vector indicates a position differencebetween a top-left sample of a current block including the currentstring and a top-left sample of a reference block including thereference string.

In the method and apparatus for decoding a video signal according to thepresent invention, the reference string is determined as a string at thesame position as the current string in a reference block specified bythe string vector.

A video signal encoding method and apparatus according to the presentinvention determines, based on a sample string matching technique, alength of a current string to be encoded in a current block, determinesa reference string based on at least one of the length of the currentstring or a string vector relating to the current string, and predictsthe current string using the determined reference string.

In the method and apparatus for encoding a video signal according to thepresent invention, the length of the current string is determined basedon the string length information.

In the method and apparatus for encoding a video signal according to thepresent invention, the string length information is encoded with mostsignificant bit information and offset information regarding the lengthof the current string.

In the method and apparatus for encoding a video signal according to thepresent invention, determining the length of the current string mayinclude determining whether the first and last samples of the currentstring belong to the same row, and encoding the string last vectorinformation for specifying the position of the last sample of thecurrent string if the first sample and the last sample of the currentstring belong to the same row.

In the method and apparatus for encoding a video signal according to thepresent invention, the string vector indicates a position differencebetween a top-left sample of a current block including the currentstring and a top-left sample of a reference block including thereference string.

In the method and apparatus for encoding a video signal according to thepresent invention, the reference string is determined as a string at thesame position as the current string in a reference block specified bythe string vector.

Advantageous Effects

According to the present invention, a palette index may be effectivelyencoded/decoded based on an index string matching technique.

According to the present invention, prediction/restoration of one ormore sample arrays may be effectively performed based on a sample stringmatching technique.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a video encoding apparatusaccording to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a video decoding apparatusaccording to an embodiment of the present invention.

FIG. 3 illustrates a method of restoring a current block based on apalette mode according to an embodiment of the present invention.

FIG. 4 illustrates a method of restrictively signaling of a reuse flag(previous_palette_entry_flag) according to an embodiment of the presentinvention.

FIG. 5 illustrates a method of signaling a reuse flag in the form of abinary vector based on a run encoding, according to an embodiment of thepresent invention.

FIG. 6 illustrates a method for restrictively obtaining a reuse flagbased on a last entry flag (last_previous_entry_flag), according to anembodiment of the present invention.

FIG. 7 illustrates a method of encoding a palette index of a currentblock based on an index string matching technique according to anembodiment of the present invention.

FIG. 8 illustrates a method of deriving a palette index of a currentblock based on an index string matching technique according to anembodiment of the present invention.

FIG. 9 illustrates a scan order in the palette mode according to anembodiment of the present invention.

FIG. 10 illustrates a schematic configuration of a sample stringmatching technique according to an embodiment of the present invention.

FIG. 11 illustrates a process of predicting/restoring a current blockbased on a sample string matching technique according to an embodimentof the present invention.

FIG. 12 illustrates a method of deriving a length of a current stringbased on whether or not the first sample and the last sample of acurrent string exist in the same row, according to an embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A video signal decoding method and apparatus according to the presentinvention determines, based on a sample string matching technique, alength of a current string to be decoded in a current block anddetermines a reference string based on at least one of a length of thecurrent string or a string vector relating to the current string, andpredict the current string using the determined reference string.

In the method and apparatus for decoding a video signal according to thepresent invention, the length of the current string is determined basedon the encoded string length information.

In the method and apparatus for decoding a video signal according to thepresent invention, the step of determining the length of the currentstring may include obtaining a string row flag (string_same_row_flag)for the current string from a bitstream, obtaining, based on the stringrow flag, the string last vector information for specifying the positionof the last sample of the current string from the bitstream, anddetermining a length of the current string based on the position of thefirst sample of the current string and the obtained string last vectorinformation.

In the method and apparatus for decoding a video signal according to thepresent invention, the string row flag indicates whether the firstsample and the last sample of the current string belong to the same row.

In the method and apparatus for decoding a video signal according to thepresent invention, the string vector indicates a position differencebetween a top-left sample of a current block including the currentstring and a top-left sample of a reference block including thereference string.

In the method and apparatus for decoding a video signal according to thepresent invention, the reference string is determined as a string at thesame position as the current string in a reference block specified bythe string vector.

A video signal encoding method and apparatus according to the presentinvention determines, based on a sample string matching technique, alength of a current string to be encoded in a current block, determinesa reference string based on at least one of the length of the currentstring or a string vector relating to the current string, and predictsthe current string using the determined reference string.

In the method and apparatus for encoding a video signal according to thepresent invention, the length of the current string is determined basedon the string length information.

In the method and apparatus for encoding a video signal according to thepresent invention, the string length information is encoded with mostsignificant bit information and offset information regarding the lengthof the current string.

In the method and apparatus for encoding a video signal according to thepresent invention, determining the length of the current string mayinclude determining whether the first and last samples of the currentstring belong to the same row, and encoding the string last vectorinformation for specifying the position of the last sample of thecurrent string if the first sample and the last sample of the currentstring belong to the same row.

In the method and apparatus for encoding a video signal according to thepresent invention, the string vector indicates a position differencebetween a top-left sample of a current block including the currentstring and a top-left sample of a reference block including thereference string.

In the method and apparatus for encoding a video signal according to thepresent invention, the reference string is determined as a string at thesame position as the current string in a reference block specified bythe string vector.

MODE FOR CARRYING OUT THE INVENTION

The present invention may be changed and modified variously and beillustrated with reference to different exemplary embodiments, some ofwhich will be described and shown in the drawings. However, theseembodiments are not intended for limiting the invention but areconstrued as including includes all modifications, equivalents andreplacements which belong to the spirit and technical scope of theinvention. Like reference numerals in the drawings refer to likeelements throughout.

Although the terms first, second, etc. may be used to describe variouselements, these elements should not be limited by these terms. Theseterms are used only to distinguish one element from another element. Forexample, a first element could be termed a second element and a secondelement could be termed a first element likewise without departing fromthe teachings of the present invention. The term “and/or” includes anyand all combinations of a plurality of associated listed items.

It will be understood that when an element is referred to as being“connected to” or “coupled to” another element, the element can bedirectly connected or coupled to another element or interveningelements. On the contrary, when an element is referred to as being“directly connected to” or “directly coupled to” another element, thereare no intervening elements present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include” and/or“have,” when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Hereinafter, exemplary embodiments of the invention will be described indetail with reference to the accompanying drawings. Like referencenumerals in the drawings refer to like elements throughout, andredundant descriptions of like elements will be omitted herein.

FIG. 1 is a block diagram illustrating a video encoding apparatusaccording to an embodiment of the present invention.

Referring to FIG. 1, the video encoding apparatus 100 includes a picturedividing unit 110, prediction units 120 and 125, a transform unit 130, aquantization unit 135, a reordering unit 160, an entropy encoding unit165, an inverse quantization unit 140, an inverse transform unit 145, afilter unit 150, and a memory 155.

Each of the elements shown in FIG. 1 is shown independently to representdifferent characteristic functions in the video encoding apparatus, anddoes not mean that each element is composed of separate hardware or onesoftware configuration unit. That is, the elements are independentlyarranged for convenience of description, wherein at least two elementsmay be combined into a single element, or a single element may bedivided into a plurality of elements to perform functions. It is to benoted that embodiments in which some elements are integrated into onecombined element and/or an element is divided into multiple separateelements are included in the scope of the present invention withoutdeparting from the essence of the present invention.

Some elements are not essential to the substantial functions in theinvention and may be optional constituents for merely improvingperformance. The invention may be embodied by including onlyconstituents essential to embodiment of the invention, except forconstituents used to merely improve performance. The structure includingonly the essential constituents except for the optical constituents usedto merely improve performance belongs to the scope of the invention.

The picture dividing unit 110 may divide an input picture into at leastone processing unit. Here, the processing unit may be a prediction unit(PU), a transform unit (TU) or a coding unit (CU). The picture dividingunit 110 may divide one picture into a plurality of combinations of CUs,PUs and TUs and encode the picture by selecting one combination of CUs,PUs and TUs on the basis of a predetermined criterion (for example, acost function).

For example, one picture may be partitioned into a plurality of CUs. Arecursive tree structure, such as a quad tree structure, may be used topartition a picture into CUs. A CU, for which a picture or a CU of amaximum size may be as root, may be partitioned into sub-coding unitswith as many child nodes as the partitioned CUs. A CU which is notpartitioned any more in accordance with a predetermined limitation is aleaf node. That is, assuming that a CU may be partitioned into quadrantsonly, a single CU may be partitioned into at most four different CUs.

In the embodiments of the invention, a CU may be used to refer to notonly a unit of encoding but also a unit of decoding.

A PU may be partitioned into at least one square or rectangular formwith the same size in a CU. For PUs partitioned from a same CU, a PU mayhave different shape and/or size from another PU.

When a PU for intra prediction is generated based on a CU and the CU isnot a minimum CU, the CU may be subjected to intra prediction withoutbeing partitioned into plural PUs (N×N).

The prediction units 120 and 125 may include an inter prediction unit120 to perform inter prediction and an intra prediction unit 125 toperform intra prediction. The prediction units 120 and 125 may determinewhich of inter prediction and intra prediction is performed on a PU, andmay determine specific information (for example, an intra predictionmode, a motion vector, and a reference picture) of the determinedprediction method. Here, a processing unit on which prediction isperformed may be different from a processing unit for which a predictionmethod and specific information thereon are determined. For example, aprediction method and a prediction mode may be determined for each PU,while prediction may be performed for each TU. A residual value(residual block) between a generated predicted block and an originalblock may be input to the transform unit 130. Further, prediction modeinformation, motion vector information and the like used for predictionmay be encoded along with the residual value by the entropy encodingunit 165 and be transmitted to the decoding apparatus. When a specificencoding mode is used, the original block may be encoded and transmittedto the decoding apparatus without generating a prediction block by theprediction units 120 and 125.

The inter prediction unit 120 may predict a PU based on information onat least one picture among a previous picture of a current picture and asubsequent picture of a current picture. In some cases, the interprediction unit 120 may predict a PU based on information of a partiallyencoded region in the current picture. The inter prediction unit 120 mayinclude a reference picture interpolation unit, a motion predictionunit, and a motion compensation unit.

The reference picture interpolation unit may be supplied with referencepicture information from the memory 155 and generate pixel informationless than or equal to an integer pixel on a reference picture. In thecase of luma pixels, a DCT-based 8-tap interpolation filter with avariable filter coefficient may be used to generate pixel informationless than or equal to an integer pixel in a unit of a ¼ pixel. In thecase of chroma pixels, a DCT-based 4-tap interpolation filter with avariable filter coefficient may be used to generate pixel informationless than or equal to an integer pixel in a unit of a ⅛ pixel.

The motion prediction unit may perform motion prediction on the basis ofthe reference picture interpolated by the reference pictureinterpolation unit. Various methods, such as a full search-based blockmatching algorithm (FBMA), a three-step search (TSS) algorithm and a newthree-step search (NTS) algorithm, may be used to calculate a motionvector. A motion vector has a motion vector value in the unit of a ½ or¼ pixel on the basis of an interpolated pixel. The motion predictionunit may predict a current PU using different motion prediction methods.Various methods, such as skip mode, merge mode, and advanced motionvector prediction (AMVP) mode, intra block copy mode, etc. may be usedas the motion prediction method.

The intra prediction unit 125 may generate a PU on the basis ofinformation on a reference pixel neighboring to a current block. When areference pixel is a pixel for which inter prediction has been performedbecause a block neighboring to the current PU is a block for which interprediction has been performed, information on a reference pixel in theblock for which inter prediction has been performed may be replaced withinformation on a reference pixel in a block for which intra predictionhas been performed. That is, when a reference pixel is not available,information on the unavailable reference pixel may be replaced withinformation on at least one reference pixel of the available referencepixels.

A prediction mode of intra prediction includes a directional predictionmode in which reference pixel information is used according to aprediction direction and a non-directional prediction mode in whichinformation on direction is not used in performing prediction. A modefor predicting luma information and a mode for predicting chromainformation may be different from each other. Further, intra predictionmode information used to obtain luma information or predicted lumasignal information may be used to predict chroma information.

When a PU and a TU have the same size, intra prediction on the PU may beperformed based on a left pixel, an upper-left pixel and an upper pixelof the PU. On the other hand, when a PU and a TU have different sizes,intra prediction may be performed by using reference pixels which aredetermined based on the TU. Intra prediction using N×N partitioning maybe performed only for a minimum CU.

In the intra prediction method, a predicted block may be generated byapplying an adaptive intra smoothing (AIS) filter to the referencepixels according to the prediction mode. Different types of AIS filtersmay be applied to the reference pixels. In the intra prediction method,the intra prediction mode of a current PU may be predicted from an intraprediction mode of a PU neighboring to the current PU. In predicting theprediction mode of the current PU using mode information predicted froma neighboring PU, when the current PU and the neighboring PU have thesame intra prediction mode, information indicating that the current PUand the neighboring PU have the same prediction mode may be transmittedusing predetermined flag information. When the current PU and theneighboring PU have different prediction modes, information on theprediction mode of the current block may be encoded by entropy encoding.

A residual block including residual information may be generated. Theresidual information is a difference between the original block of thePU and the predicted block of a PU generated by the prediction units 120and 125. The generated residual block may be input to the transform unit130.

The transform unit 130 may transform the residual block using atransform method such as Discrete Cosine Transform (DCT), Discrete SineTransform (DST) or KLT. The residual block includes information on theresidual between the PU generated by the prediction units 120 and 125and the original block. A transform method to be used to transform theresidual block may be determined among DCT, DST and KLT on the basis ofthe information on the intra prediction mode of the PU which is used togenerate the residual block.

The quantization unit 135 may quantize values transformed into afrequency domain by the transform unit 130. A quantization coefficientmay be changed depending on a block or importance of an image. Valuesoutput from the quantization unit 135 may be provided to thedequantization unit 140 and the rearrangement unit 160.

The rearrangement unit 160 may rearrange quantized coefficients.

The rearrangement unit 160 may change a two-dimensional (2D) block ofcoefficients into a one-dimensional (1D) vector of coefficients throughcoefficient scanning. For example, the rearrangement unit 125 may changea 2D block of coefficients into a 1D vector of coefficients by scanningfrom DC coefficients to coefficients of a high frequency domain usingzigzag scanning. Vertical scanning for scanning a 2D block ofcoefficients in a vertical and horizontal scanning for scanning a 2Dblock of coefficients in a horizontal direction may be used depending ona size of a TU and an intra prediction mode, instead of zigzag scanning.That is, a scanning method may be selected based on the size of the TUand the intra prediction mode, among zigzag scanning, vertical scanning,and horizontal scanning.

The entropy encoding unit 165 may perform entropy encoding on the basisof the values obtained by the rearrangement unit 160. Various encodingmethods, such as exponential Golomb coding, context-adaptive variablelength coding (CAVLC), or context-adaptive binary arithmetic coding(CABAC), may be used for entropy encoding.

The entropy encoding unit 165 may encode a variety of information, suchas residual coefficient information and block type information on a CU,prediction mode information, partitioning unit information, PUinformation, transfer unit information, motion vector information,reference frame information, block interpolation information andfiltering information from the rearrangement unit 160 and the predictionunits 120 and 125.

The entropy encoding unit 165 may entropy-encode coefficients of a CUinput from the rearrangement unit 160.

The dequantization unit 140 and the inverse transform unit 145dequantize the values which are quantized by the quantization unit 135and inverse-transform the values which are transformed by the transformunit 130. A reconstructed block may be generated by adding the residualvalues to the predicted PU. The residual values may be generated by thedequantization unit 140 and the inverse transform unit 145. Thepredicted PU may be predicted by the motion vector prediction unit, themotion compensation unit, and the intra prediction unit of theprediction units 120 and 125.

The filter unit 150 may include at least one of a deblocking filter, anoffset unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion generated byboundaries between blocks in a reconstructed picture. Whether to applythe deblocking filter to a current block may be determined on the basisof pixels included in several rows or columns of the block. When thedeblocking filter is applied to a block, a strong filter or a weakfilter may be applied depending on a required deblocking filteringstrength. When horizontal filtering and vertical filtering are performedin applying the deblocking filter, the horizontal filtering and verticalfiltering may be performed in parallel.

The offset unit may apply the offset with respect to the original imageto the deblocking filtered image, in units of pixels. A region to whichthe offset may be applied may be determined after partitioning pixels ofa picture into a predetermined number of regions. The offset may beapplied to the determined region in consideration of edge information oneach pixel or the method of applying the offset to the determinedregion.

The ALF may perform filtering based on a comparison result of thefiltered reconstructed image and the original image. Pixels included inan image may be partitioned into predetermined groups, a filter to beapplied to each group may be determined, and differential filtering maybe performed for each group. Information on whether to apply the ALF maybe transferred by each coding unit (CU) and a shape and filtercoefficients of an ALF to be applied to each block may vary. Further, anALF with the same form (fixed form) may be applied to a block regardlessof characteristics of the block.

The memory 155 may store a reconstructed block or picture output fromthe filter unit 150, and the stored reconstructed block or picture maybe supplied to the prediction units 120 and 125 when performing interprediction.

FIG. 2 is a block diagram illustrating a video decoding apparatusaccording an exemplary embodiment of the present invention.

Referring to FIG. 2, the video decoding apparatus 200 may include anentropy decoding unit 210, a rearrangement unit 215, a dequantizationunit 220, an inverse transform unit 225, prediction units 230 and 235, afilter unit 240, and a memory 245.

When a video bitstream is input from the video encoding apparatus, theinput bitstream may be decoded according to an inverse process of thevideo encoding process performed in the video encoding apparatus.

The entropy decoding unit 210 may perform entropy decoding according toan inverse process of the entropy encoding process by the entropyencoding unit of the video encoding apparatus. For example, variousmethods, such as exponential Golomb coding, CAVLC or CABAC, may be usedfor entropy encoding, corresponding to the method used by the videoencoding apparatus.

The entropy decoding unit 210 may decode information associated withintra prediction and inter prediction performed by the encodingapparatus.

The rearrangement unit 215 may perform rearrangement on the bitstreamentropy-decoded by the entropy decoding unit 210 on the basis of therearrangement method of the encoding unit. The rearrangement unit 215may reconstruct and rearrange coefficients of a 1D vector form intocoefficients of a 2D block. The rearrangement unit 215 may be providedwith information on coefficient scanning performed by the encodingapparatus and may perform rearrangement using a method of inverselyscanning the coefficients, on the basis of scanning order performed bythe encoding apparatus.

The dequantization unit 220 may perform dequantization on the basis of aquantization parameter provided from the encoding apparatus and therearranged coefficients of the block.

The inverse transform unit 225 may perform inverse transform performedby the transform unit (that is, inverse DCT, inverse DST or inverse KLT)on a result of quantization performed by the video encoding apparatus.Inverse transform may be performed on the basis of a transfer unitdetermined by the video encoding apparatus. The transform unit 225 ofthe video decoding apparatus may selectively perform the transformscheme (e.g., DCT, DST, KLT) depending on a plurality of informationelements, such as a prediction method, a size of the current block and aprediction direction, etc.

The prediction units 230 and 235 may generate a prediction block on thebasis of information for generating prediction block and information ona previously-decoded block or picture provided. The information forgenerating prediction block may be provided from the entropy decodingunit 210. The information on a previously-decoded block or picture maybe provided from the memory 245

Similarly to the operation of the video encoding apparatus as describedabove, when a PU and a TU have the same size, intra prediction on the PUis performed based on left pixels, an upper-left pixel and upper pixelsof the PU. On the other hand, when a PU and a TU have different sizes,intra prediction may be performed using reference pixels which aredetermined based on the TU. Intra prediction using N×N partitioning maybe used only for a minimum CU.

The prediction units 230 and 235 may include a PU determination unit, aninter prediction unit and an intra prediction unit. The PU determinationunit may receive a variety of information, such as PU information,prediction mode information on an intra prediction method and motionprediction-related information on an inter prediction method, etc. fromthe entropy decoding unit 210, may determine a PU for a current CU. ThePU determination unit may determine which of the inter prediction andthe intra prediction is performed on the PU. An inter prediction unit230 may perform inter prediction on a current PU on the basis ofinformation on at least one picture among a previous picture and asubsequent picture of a current picture including the current PU. Aninter prediction unit 230 may use information necessary for interprediction for the current PU provided from the video encodingapparatus. The inter prediction may be performed on the basis of theinformation of the pre-reconstructed partial region in the currentpicture including the current PU.

In order to perform inter prediction, it may be determined, in an unitof a CU, whether a motion prediction method for a PU included in the CUis a skip mode, a merge mode, an AMVP mode or intra block copy mode.

An intra prediction unit 235 may generate a prediction block on thebasis of pixel information in a current picture. When a PU is a PU forwhich intra prediction is performed, intra prediction may be performedbased on intra prediction mode information on the PU provided from thevideo encoding apparatus. The intra prediction unit 235 may include anAIS (Adaptive Intra Smoothing) filter, a reference pixel interpolationunit, and a DC filter. The AIS filter performs filtering on referencepixels of a current block. The AIS filter may decide whether to applythe filter or not, depending on a prediction mode for the current PU.AIS filtering may be performed on the reference pixels of the currentblock using the prediction mode for the PU and information on the AISfilter provided from the video encoding apparatus. When the predictionmode for the current block is a mode not performing MS filtering, theAIS filter may not be applied.

When the prediction mode for the PU indicates a prediction mode ofperforming intra prediction on the basis of pixel values obtained byinterpolating the reference pixels, the reference pixel interpolationunit may generate reference pixels in a unit of a fractional pixel lessthan an integer pixel (i.e. full pixel) by interpolating the referencepixels. When the prediction mode for the current PU indicates aprediction mode of generating a prediction block without interpolatingthe reference pixels, the reference pixels may not be interpolated. TheDC filter may generate a prediction block through filtering when theprediction mode for the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit240. The filter unit 240 includes a deblocking filter, an offset unit,and an ALF.

The video encoding apparatus may provide information on whether thedeblocking filter is applied to a corresponding block or picture, andinformation on which of a strong filter and a weak filter is appliedwhen the deblocking filter is used. The deblocking filter of the videodecoding apparatus may be provided with information on the deblockingfilter from the video encoding apparatus and may perform deblockingfiltering on a corresponding block.

The offset unit may apply offset to the reconstructed picture on thebasis of information on an offset type and offset value applied to thepicture in the encoding process.

The ALF may be applied to a CU on the basis of information on whetherthe ALF is applied and ALF coefficient information, etc. provided fromthe encoding apparatus. The ALF information may be included and providedin a specific parameter set.

The memory 245 may store the reconstructed picture or block for use as areference picture or a reference block and may provide the reconstructedpicture to an output unit.

As described above, in the embodiments of the invention, the term“coding unit” is used as an encoding unit for a convenience ofdescriptions. However, the term “coding unit” may be also used as a unitof decoding.

FIG. 3 illustrates a method of restoring a current block based on apalette mode according to an embodiment of the present invention.

In the case of an image including an animation or a graphic, it mayhappen that all or a part of the image is composed of only a specificpixel value. In this case, a method of encoding a specific pixel valueconstituting the area may be used without using an inter prediction orintra prediction method, which is called a palette mode. The palettemode may be applied in a block unit (for example, a coding unit, aprediction unit). For this purpose, flag information (palette_mode_flag)indicating whether the palette mode is used may be signaled on a blockbasis.

Referring to FIG. 3, a palette map for a current block encoded in apalette mode may be constructed (S300).

The palette map may comprise at least one palette entry and a map indexidentifying each palette entry. The palette map of the current block canbe derived from a palette map of the previous block (hereinafterreferred to as a previous palette map). Here, the previous block maymean a block that has been encoded or decoded before the current block.

The palette entry of the current block may comprise at least one of apredicted palette entry or a signaled palette entry. The current blockmay use all or a part of the palette entries used by the previous block.A predicted palette entry may be representative of the palette entryreused in the current block among the palette entries used in theprevious block.

Specifically, the current block may use the same palette map as theprevious block. For this, a flag (palette_share_flag) indicating whetherthe current block uses the same palette map as the previous block may besignaled. Here, the same palette map means that the size of the palettemap (or the number of palette entries included in the palette map) isthe same and the palette entries included in the palette map are thesame. When the value of palette_share_flag is 1, the current block usesthe same palette map as the previous block. When the value of thepalette_share_flag is 0, the current block may use the palette map inwhich at least one of the size of the palette map or the palette entriesincluded in the palette map is different from that of the neighboringblock.

Alternatively, the current block may selectively use some paletteentries of the previous palette map. For this purpose, a flag(previous_palette_entry_flag, hereinafter referred to as a reuse flag)for specifying whether the palette entry is reused may be used.Specifically, the value of the reuse flag is assigned to each of thepalette entries of the previous palette map. The reuse flag(previous_palette_entry_flag [i]) indicates that the palette entrycorresponding to the map index i in the previous palette map is reusedor not. For example, if the value of the reuse flag is 1, the paletteentry corresponding to the map index i in the previous palette map isreused in the palette map of the current block. Otherwise, it is notreused. A palette map of the current block may be constructed byextracting palette entries having a reuse flag equal to 1 from theprevious pallet map and sequentially arranging the palette entries. Thereuse flag may be signaled in the form of a flag encoded for eachpalette entry, or may be signaled in the form of a binary vector basedon a run encoding, which will be described in detail with reference toFIG. 4 to FIG. 6.

In order to selectively use some of the palette entries in the palettemap of the previous block, a re-use variable array(predictor_palette_entry_reuse_flag) for specifying whether the previouspalette entry is reused and a syntax palette_predictor_run value forspecifying the number of reuse variables equal to 0 between non-zeroreuse variables in the reuse variable array may be used.

In addition, the palette map of the current block may further include asignaled palette entry signaled from the bitstream. Here, the signaledpalette entry includes a palette entry that is not included in theprevious palette map, among the palette entries used by the currentblock.

Referring to FIG. 3, a palette index may be derived according to apredetermined scan order in a sample unit (or pixel unit) of the currentblock (S310).

As the scan order of the present invention, a horizontal scan, avertical scan, a horizontal traverse scan, a vertical traverse scan, orthe like may be used, and this will be described in detail withreference to FIG. 9.

The first flag information (first_palette_idx_flag) indicates whetherthe current index is a palette index used in the current decodingbuffer. The palette index information (palette_idx) is encoded tospecify a palette index used in the current block. A palette index ofthe current block may be derived using at least one of first flaginformation, palette index information, palette index run information(palette_idx_run), or index distance information(distance_minus1_from_used_idx). This method will be referred to as anindex string matching technique. Here, the palette index run informationmay mean the number of the remaining palette indices excluding thepalette index which is generated first, among consecutive paletteindices having the same value. Alternatively, the palette index runinformation may mean a position difference or a scan order differencebetween the first palette index and the last palette index amongconsecutive palette indices having the same value. The index distanceinformation may be encoded to specify a position of a previous samplehaving the same palette index as the current sample. Here, the previoussample may be a sample having a scan order earlier than the currentsample, and a sample having the last scan order among the samples havingthe same palette index as the current sample.

A method of encoding/decoding the palette index of the current blockbased on the index string matching technique will be described in detailwith reference to FIGS. 7 and 8.

Referring to FIG. 3, a sample of a current block may be restored basedon the palette index derived in step S310 (S320).

Specifically, the sample of the current block may be restored based onthe palette map of the current block configured in step S300 and thepalette index derived in step S310. A palette entry having a map indexof the same value as the derived palette index is extracted from thepalette map of the current block, and then the sample of the currentblock may be restored using the palette entry. For example, the value ofthe palette entry extracted from the palette map may be set to thepredicted value or the restored value of the sample of the currentblock.

However, the value of the derived palette index may be equal to thenumber of palette entries constituting the palette map of the currentblock. In this case, the sample of the current block can be restored byusing the palette entry of the palette map configured in step S300. Thatis, since the map index of the palette map has a value between 0 (thenumber of palette entries−1), the value of the derived palette indexequal to the number of palette entries means that there is no paletteentry corresponding to the derived palette index in the palette mapconfigured in step S300. In this way, when a sample having a paletteindex of the same value as the number of palette entries in the currentblock exists, the sample may be determined to be encoded in an escapemode (ESCAPE MODE). Here, the escape mode may refer to a method ofrestoring a sample value based on a palette escape value that isadditionally signaled, instead of using the palette entry of the palettemap constructed in step S300. Thus, a sample having a palette indexequal to the number of palette entries may be restored using theadditionally signaled palette escape value.

On the other hand, the escape mode may be adaptively used based on thenumber of palette entries constituting the palette map of the currentblock. Here, the number of palette entries may be derived as the sum ofthe number of palette entries predicted from the palette map of theprevious block and the number of signaled palette entries. The predictedpalette entry and the signaled palette entry are as described withreference to FIG. 3. For example, if the number of palette entries usedby the current block is greater than zero (e.g., if the number ofpalette entries is one), restoring at least one sample of the currentblock based on the escape mode may be allowed. Conversely, if the numberof palette entries used by the current block is zero, the current blockis not allowed to be restored based on the escape mode.

FIG. 4 illustrates a method of signaling of a reuse flag(previous_palette_entry_flag) according to an embodiment of the presentinvention.

Referring to FIG. 4, the reuse number information (num_previous_paletteentry) related to the palette map of the current block may be obtainedfrom the bitstream (S400).

Here, the reuse number information may mean information encoded toindicate the number of palette entries reused as palette entries of thecurrent block among the palette entries of the previous palette map.

A reuse flag (previous_palette_entry_flag [i]) specifying whether or notthe i-th palette entry is to be reused may be obtained from thebitstream (S410).

The reuse flag is signaled by the size of the previous palette map (orthe number of palette entries included in the previous palette map).Here, i corresponds to a map index that identifies the palette entry ofthe previous palette map, and the value of i is in a range 0 to (size ofthe previous palette map-1).

It may be checked whether the value of the reuse flag obtained in stepS410 is 1 (S420). As a result of checking, if the value of the reuseflag is 1, a variable numPredPreviousPalette indicating the number ofreuse flags equal to 1 may be updated (S430). For example, the value ofthe variable numPredPreviousPalette may be increased by one.

On the other hand, if the value of the reuse flag is 0, a reuse flag(previous_palette_entry_flag [i+1]) specifying whether to reuse the(i+1)-th palette entry may be obtained from the bitstream (S410).

It is possible to compare whether the variable numPredPreviousPalettevalue increased in step S430 and the reuse number information obtainedin step S400 are the same (S440).

If the variable numPredPreviousPalette is not equal to the numberinformation obtained in step S400, a reuse flag(previous_palette_entry_flag [i+1]) specifying whether to reuse the(i+1)-th palette entry may be obtained from the bitstream (S410).However, if the variable numPredPreviousPalette is equal to the numberinformation obtained in step S400, a palette entry having a map indexgreater than the i value may not be used as a palette entry of thecurrent block. For this, if the variable numPredPreviousPalette is equalto the number information obtained in step S400, the value of i may bederived to be equal to or larger than the size of the previous palettemap. For example, the value of i may be derived by adding 1 to the sizeof the previous palette map. Thus, by setting the value of i to be equalto or greater than the size of the previous palette map, the reuse flagassociated with the (i+1)-th palette entry may not be signaled.

FIG. 5 illustrates a method of signaling a reuse flag in the form of abinary vector based on a run encoding, according to an embodiment of thepresent invention.

In the present embodiment, it is assumed that the palette map of theprevious block uses eight palette entries having a map index of 0 to 7.

For each of the palette entries of the previous block with index 0 to 7,the video encoding apparatus determines whether the palette entry isreused as a palette entry of the current block. If the palette entry isreused as a palette entry of the current block, the value of the reuseflag for the palette entry may be set to be 1, and otherwise, it may beset to be 0. For example, as shown in FIG. 5, when the palette entriesof 0, 1, 3, and 7 among the palette entries of the previous block arereused as palette entries of the current block and the remaining paletteentries are not reused, a binary vector represented by 11010001 may begenerated.

Then, at least one of the number of l's in the binary vector (i.e., thenumber of palette entries reused as a palette entry of the current blockin the previous block) or the number of zeros earlier than 1 in thebinary vector is encoded, and then it may be signaled to the videodecoding apparatus. For example, since the number of 1's in the binaryvector is 4, 4 may be encoded as the number of palette entries of theprevious block reused as the palette entry of the current block. Inaddition, the number of zeros preceding the 1 in the binary vector, thatis, 0, 0, 1, and 3, may be sequentially encoded.

The video decoding apparatus may receive, from the video encodingapparatus, at least one of information (num_previous_palette_entry)about the number of palette entries of a previous block reused aspalette entries of the current block or information (palette_entry_run)about the number of zeros preceding the 1 in the binary vector, and thenconstruct a palette map of the current block by using it.

For example, the video decoding apparatus successively extractsinformation (palette_entry_run) about the number of zeros preceding the1 in the binary vector, that is, 0, 0, 1, and 3, from the bitstream. Thebinary vector indicating whether to reuse the palette entry of aprevious block, that is, 11010001 may be restored by using the extractedinformation. When a value of 1 is generated in the process of restoringthe binary vector, the palette entry of the previous block correspondingto the value 1 may be inserted into the palette map of the currentblock. Through this process, a palette map of the current block may beconstructed by selectively reusing some palette entries from the palettemap of the previous block.

FIG. 6 illustrates a method of obtaining a reuse flag in a limitedmanner based on a last entry flag (last_previous_entry_flag) accordingto an embodiment of the present invention.

Referring to FIG. 6, a reuse flag (previous_palette_entry_flag [idx])may be obtained in consideration of the size of the palette map of theprevious block (S600).

The reuse flag may indicate whether the palette entry corresponding tothe current map index idx in the palette map of the previous block isreused as the palette entry of the current block. The reuse flag may beobtained within a range where the current map index idx is smaller thanthe size of the palette map of the previous block (or the number ofpalette entries constituting the palette map of the previous block).

The last entry flag (last_previous_entry_flag) may be obtained based onthe reuse flag obtained in step S600 (S610).

Specifically, if the value of the reuse flag is 1, the last entry flagis extracted from the bitstream, and if the value of the reuse flag is0, the last entry flag is not extracted from the bitstream.

Here, the last entry flag may indicate whether the palette entrycorresponding to the current map index idx is the last palette entry ofthe palette entries of the previous block that are reused as the paletteentry of the current block. For example, if the value of the last entryflag is 1, a palette entry having a map index value greater than thecurrent map index idx is not reused as a palette entry of the currentblock. On the other hand, if the value of the last entry flag is 0, atleast one of the palette entries having the map index value greater thanthe current map index idx may be reused as the palette entry of thecurrent block.

The value of the current map index idx may be updated to be apredetermined value based on the last entry flag obtained in step S610(S620).

For example, if the value of the last entry flag is 1, the value of thecurrent map index idx may be updated to be the same value as the size ofthe palette map of the previous block. In this case, as described above,as the reuse flag is extracted within the size range of the palette mapof the previous block, the reuse flag is not signaled for the paletteentry having the map index value greater than the current map index idx.

On the other hand, when the value of the last entry flag is 0, it meansthat at least one of palette entries having a map index greater than thecurrent map index idx may be reused as a palette entry of the currentblock. Thus, the current map index idx may be increased by one. That is,the current map index idx value is updated to (idx+1), and steps S600and S610 may be repeated until the value of the last entry flag reaches1.

Through the above-described process, the reuse flag of the presentinvention may be limitedly signaled based on the value of the last entryflag.

FIG. 7 illustrates a method of encoding a palette index of a currentblock based on an index string matching technique according to anembodiment of the present invention.

In the present embodiment, it is assumed that the current block is a 4×4block, and is composed of 16 samples. As shown in FIG. 7, the paletteindices related to the current block may be represented by anone-dimensional array according to a predetermined scan order. Here, itis assumed that the current block has an one-dimensional palette indexarray like {8, 8, 8, 15, 15, 15, 15, 2, 8, 8, 8, 8, 8, 2, 2, 2}.

The palette index of the current block is encoded according to apredetermined scan order. At this time, a palette index to be encoded isgenerated first in a sample having a scan order 0 (hereinafter referredto as a 0th sample). This may mean that the palette index 8 of the 0thsample is a palette index which is not used in the current decodingbuffer. Accordingly, the value of the first flag information(first_palette_idx_flag) indicating whether a current index is a paletteindex used in the current decoding buffer may be encoded as 1.

Then, since the palette index of the 0th sample is 8, the palette indexinformation (palette_idx) of the 0th sample may be encoded as 8. Then,the value of the palette index run information (palette_idx_run)indicating the number of the palette indices of the same valuecontinuously occurring after the 0th sample may be encoded as 2. In thismanner, the palette index from the 0th sample to the 2nd sample may beencoded using the first flag information, the palette index information,and the palette index run information.

Similarly, the 3rd sample has a palette index of 15, which is not apalette index used in the current decoding buffer. Therefore, the valueof the first flag information (first_palette_idx_flag) is encoded as 1,and the palette index information (palette_idx) of the 3rd sample isencoded as 15. Since there are three successive palette indices of thesame value after the 3rd sample, the value of the palette index runinformation (palette_idx_run) is encoded as 3.

On the other hand, the 8th sample has the palette index of 8, and thepalette index 8 corresponds to the palette index used in the currentdecoding buffer (especially, the 0th sample to the 2nd sample). In thiscase, the value of the first flag information (first_palette_idx_flag)is encoded as 0 and instead the index distance information(distance_minus1_from_used_idx) may be encoded to specify the positionof the sample where the palette index of 8 is used. As described above,the index distance information (distance_minus1_from_used_idx) isencoded to specify the position of the previous sample having the samepalette index as the current sample, where the previous sample is asample having a scan order earlier than the current sample. The previoussample may mean a sample having a last scan order, among samples havingthe same palette index as the current sample. For example, the indexdistance information may be encoded by subtracting 1 from the positiondifference between the 8th sample and the 2nd sample where the paletteindex of 8 is used previously. Then, since there are four paletteindices of the same value successively after the 8th sample, the valueof the palette index run information (palette_idx_run) may be encoded as4. In this manner, the palette indices from the 8th sample to the 12thsample may be encoded using the first flag information, the indexdistance information, and the palette index run information. It isneedless to say that the palette indices from the 13th sample to the15th sample may be encoded in the same manner.

As described above, the value of the index distance information and/orthe palette index run information may be encoded as it is, or may beencoded with two components that is, most significant bit and offset toimprove coding efficiency. Here, the offset may mean the differencebetween the value of the index distance information (or palette indexrun information) and the value corresponding to the most significant bitof the index distance information (or pallet index run information).

For example, when the value of the index distance information is 17, themost significant bit of the index distance information is 4, and theoffset becomes 1, which is the difference the index distance informationequal to 17 and 16 corresponding to the most significant bit equal to 4.Therefore, the value 17 of the index distance information may be encodedwith the most significant bit of 4 and the offset of 1.

FIG. 8 illustrates a method of deriving a palette index of a currentblock based on an index string matching technique according to anembodiment of the present invention.

Referring to FIG. 8, the first flag information (first_palette_idx_flag)regarding the current sample in the current block may be obtained fromthe bitstream (S800).

The first flag information may indicate whether the palette index of thecurrent sample is the palette index used in the current decoding buffer.The current decoding buffer may store the palette index used in theblock, in a block unit. A block unit may mean one coding block orprediction block, and may mean a block composed of a plurality of codingblocks or prediction blocks.

For example, if the value of the first flag information is 1, this mayindicate that the palette index of the current sample is not the paletteindex used in the current decoding buffer. If the value of the paletteindex is 0, it may indicate that the palette index of the current sampleis used as a palette index of another sample having a scan order beforethe current sample.

If the value of the first flag information obtained in step S800 is 1,at least one of palette index information (palette_idx) or palette indexrun information (palette_idx_run) may be obtained from the bit stream(S810).

Here, the palette index information is encoded to specify the paletteindex of the current sample, and the palette index run information maymean the number of samples in which a palette index of the same valuecontinuously occurs after the current sample. The palette index runinformation may be encoded with a most significant bit and an offset atthe video encoding apparatus. In this case, the palette index runinformation may include most significant bit information and offsetinformation relating to the palette index run.

All or some of the palette indices of the current block may be derivedbased on the palette index information and/or the palette index runinformation obtained in step S810 (S820).

Specifically, a palette index according to the palette index informationmay be allocated to the current sample, and a palette index having thesame value as the current sample may be allocated sequentially or inparallel as many as the number of samples corresponding to the paletteindex run information.

On the other hand, if the value of the first flag obtained in step S800is 0, at least one of the index distance information(distance_minus1_from_used_idx) or the palette index run information(palette_idx_run) may be obtained from the bitstream (S830).

Herein, the index distance information is encoded to specify theposition of the previous sample having the same palette index as thecurrent sample. The previous sample is a sample having a scan orderearlier than the current sample. The previous sample may mean a samplehaving a last scan order, among samples having the same palette index asthe current sample. The palette index run information is as described instep S810.

Also, the index distance information and/or the palette index runinformation may be encoded with a most significant bit and an offset atthe video encoding apparatus. In this case, the index distanceinformation and/or the palette index run information may also becomposed of most significant bit information and offset information.

All or some of the palette indices of the current block may be derivedbased on the index distance information and/or the palette index runinformation obtained in step S830 (S840).

Specifically, a previous sample having a palette index of the same valueas the current sample may be specified based on the index distanceinformation. A palette index of the specified previous sample may beassigned to the current sample. Then, a palette index having the samevalue as the current sample may be allocated sequentially or in parallelas many as the number of samples corresponding to the palette index runinformation.

FIG. 9 illustrates a scan order used in the palette mode according to anembodiment of the present invention.

Referring to FIG. 9, the scan order used in the palette mode includes ahorizontal scan, a vertical scan, a horizontal traverse scan, and avertical traverse scan.

Specifically, the horizontal scan is a method of scanning each row ofthe current block from left to right, and the vertical scan is a methodof scanning each column of the current block from top to bottom.

The horizontal traverse scan is a method of scanning the odd rows of thecurrent block from left to right and the even rows from right to left. Avertical traverse scan is a method in which odd columns of the currentblock is scanned from top to bottom while an even columns are scannedfrom bottom to top.

However, in this embodiment, it is assumed that the upper-left sample ofthe current block is set to be the scan start position, but the presentinvention is not limited to this, and another corner sample of thecurrent block may be set to be the scan start position.

FIG. 10 shows a schematic configuration of a sample string matchingtechnique according to an embodiment of the present invention.

A series of samples of a predetermined length in the current block(hereinafter referred to as string) may be predicted/restored byreferring to a sample dictionary composed of samples restored before thecurrent image to be decoded or successive samples in the reconstructedimage of the current picture

Referring to FIG. 10, a reference string may be specified using thelength of a current string and a string vector indicating a positiondifference between a reference string and a current string. A sample ofa current string may be predicted or restored by using the specifiedreference string. This method will hereinafter be referred to as asample string matching technique.

The sample dictionary may include one or more reference stringcandidates and may include an index for identifying each referencestring candidate. A reference string candidate may refer to a set of oneor more pixels.

The sample dictionary may be updated by adding or deleting all or somereference string candidates in the process of restoring the currentimage.

For example, a reference string referenced by a neighboring blockadjacent to the current block may be added as a reference stringcandidate of the current block. Alternatively, a reference stringcandidate of the current block may be specified based on the length ofthe string and/or offset which the neighboring block uses to specify thereference string, and this may be added to the sample dictionary.

Alternatively, a reference string candidate belonging to a differenttile than the current block or belonging to another slice (or slicesegment) may be removed from the sample dictionary for the currentblock. If the current block is divided into a plurality of partitionsaccording to the partition mode, the reference string candidate used byone of the plurality of partitions may be removed from the sampledictionary for another partition.

FIG. 11 illustrates a process of predicting/restoring a current blockbased on a sample string matching technique according to an embodimentof the present invention.

Referring to FIG. 11, a length of a current string to be decoded in acurrent block may be determined based on a sample string matchingtechnique (S1100).

Specifically, the video encoding apparatus may limit the minimum lengthof a string for sample string matching. For example, a string of alength equal to 1 may be restricted from being used in sample stringmatching. In this case, the video encoding apparatus may determine thelength of the current string, encode the string length information(dic_pred_length_minus2) by subtracting 2 from the determined length ofthe current string, and signal it to the video decoding apparatus.

The video decoding apparatus may derive the length of the current stringby adding 2 to the string length information (dic_pred_length_minus2)received from the video encoding apparatus. However, when a string of alength equal to 1 is used in sample string matching, the video encodingapparatus may determine the length of the current string, encode thestring length information (dic_pred_length_minus1) by subtracting 1 fromthe determined length of the current string, and signal it to the videodecoding apparatus. In this case, the video decoding apparatus mayderive the length of the current string by adding 1 to the string lengthinformation (dic_pred_length_minus1) received from the video encodingapparatus.

However, the present invention is not limited to this, and the videoencoding apparatus may variably set the minimum length of the string forsample string matching and limit the maximum length of the string usedfor sample string matching.

The string length information (for example, dic_pred_length_minus2 anddic_pred_length_minus1) may be encoded with a value(string_len_div_width) divided by the width of the current block and theremaining value (string_len_refine). In this case, the video decodingapparatus may receive the string_len_div_width and string_len_refinefrom the video encoding apparatus, and derive the string lengthinformation as shown in the following Equation 1.String lengthinformation=string_len_div_width*width+string_len_refine  [Equation 1]

Alternatively, the string length information may be encoded with twocomponents, the most significant bit and the offset for the value of thestring length information. Here, the offset may mean a differencebetween a value of the string length information and a valuecorresponding to the most significant bit.

For example, when the value of the string length information is 18, themost significant bit of the string length information is encoded as 4,and the offset is encoded as 2, which is a difference of the stringlength information equal to 18 and 16 being a value corresponding to themost significant bit equal to 4.

In this case, the video decoding apparatus may receive the mostsignificant bit information (string_len_msb) and offset information(string_len_offset) from the video encoding apparatus, and derive thestring length information as shown in the following Equation 2.String length information=1<<string_len_msb+string_len_offset  [Equation2]

The length of the current string may be derived by considering whetherthe first and last samples of the current string are present in the samerow. This will be described in detail with reference to FIG. 12.

Referring to FIG. 11, a reference string may be determined based on astring vector relating to a current string (S1110).

Here, the string vector is information encoded to specify a referencestring referenced by the current string, and may represent a positiondifference between the current string and the reference string. Forexample, a string vector may refer to a position difference between atop-left sample of a current block including a current string and atop-left sample of a reference block including a reference string. Inthis case, the current string specifies a reference block including thereference string based on the string vector, and a string at the sameposition as the current string in the specified reference block may bedetermined as a reference string.

Alternatively, the string vector may mean the position differencebetween the top-left sample of the current block including the currentstring and the first sample of the reference string, or the positiondifference between the first sample of the current string and the firstsample of the reference string.

On the other hand, the video encoding apparatus may encode the stringvector information (string_vector) by encoding the string vector of thecurrent string as it is. In this case, the video decoding apparatus mayderive the string vector based on the signaled string vector information(string_vector) from the video encoding apparatus.

Alternatively, the video encoding apparatus may encode the string vectorwith a value (string_vector_div_width) obtained by dividing the stringvector by the width of the current block and its remaining value(string_vector_refine). In this case, the video decoding apparatus mayderive a string vector based on signal_vector_div_width andstring_vector_refine signaled from the video encoding apparatus. Forexample, the string vector may be derived as shown in Equation 3.Stringvector=string_vector_div_width*width+string_vector_refine  [Equation 3]

Alternatively, the video encoding apparatus may encode the string vectorwith a most significant bit (string_vector_msb) and an offset(string_vector_offset) for the value of the string vector. Here, theoffset may mean a difference between a value of the string vector and avalue corresponding to the most significant bit. In this case, the videodecoding apparatus may derive a string vector using signal_vector_msband string_vector_offset signaled from the video encoding apparatus. Forexample, the string vector may be derived as shown in Equation 4.String vector=1<<signal_vector_msb+string_vector_offset  [Equation 4]

The reference string of the present invention may be included in thesame picture as the current string. The reference string may refer toone or more sample arrays which restored before the current string.However, the present invention is not limited to this, and the referencestring may be included in the reference picture restored before thecurrent picture and stored in the buffer.

In addition, the reference string may have the same length and/or shapeas the current string. For this, the reference string may be determinedusing the length of the current string determined in step S1100.Alternatively, a predetermined scaling factor may be applied to thereference string to have the same length and/or shape as the currentstring. An interpolation filter or sub-sampling filter may be applied tothe reference string to have the same length and/or shape as the currentstring.

Referring to FIG. 11, the current string may be predicted/restored usingthe reference string determined in step S1110 (S1120).

Specifically, a predicted sample of the current string may be obtainedbased on a reconstructed sample of the reference string. In this case,the residual sample for the current string may be signaled through thebitstream. The current string may be restored using the residual sampleand the predicted sample of the current string.

Alternatively, the restored sample of the reference string may be set tobe the restored sample of the current string.

FIG. 12 illustrates a method of deriving a length of a current stringbased on whether or not the first sample and the last sample of acurrent string exist in the same row, according to an embodiment of thepresent invention.

Referring to FIG. 12, a string row flag (string_same_row_flag) may beobtained from the bit stream (S1200).

Here, the string row flag may indicate whether the first sample and thelast sample of the current string belong to the same row. For example,if the value of the string row flag is 1, the first and last samples ofthe current string belong to the same row, and if the value of thestring row flag is 0, the first and last samples of the current stringmay not belong to the same row.

Referring to FIG. 12, if the value of the string row flag is 1, thestring length information relating to the current string may be obtainedfrom the bit stream (S1210).

The string length information in this embodiment is encoded to specifythe length of the current string, and has been described in detail withreference to FIG. 11, but a detailed description thereof will beomitted.

The length of the current string may be derived based on the stringlength information obtained in step S1210 (S1220).

On the other hand, if the value of the string row flag is 0, the stringlast vector information (string_last_vector_X, string_last_vector_Y) forspecifying the position of the last sample of the current string may beobtained from the bitstream (S1230).

Here, the string last vector may indicate the position differencebetween the top-left sample of the current block and the last sample ofthe current string, or the position difference between the first sampleand the last sample of the current string.

If the first and last samples of the current string belong to differentrows, the y component of the string last vector information is greaterthan or equal to one. Therefore, the video encoding apparatus mayperform encoding a value obtained by subtracting 1 from the y componentof the string last vector and signaling it. The video decoding apparatusmay reconstruct the y component by adding 1 to the signalized stringlast vector information (string_last_vector_Y_minus1).

The length of the current string may be derived based on the string lastvector information obtained in step S1230 (S1240).

Specifically, the position of the last sample of the current string isspecified by the string last vector information, and the length from thefirst sample to the last sample of the current string may be derived.Here, the position of the first sample of the current string may bederived based on the position of the last sample of the previous string.

INDUSTRIAL AVAILABILITY

The present invention can be used to code a video signal.

The invention claimed is:
 1. A method of decoding a video signal, themethod comprising: determining a length of a current string to bedecoded in a current block, based on a sample string matching technique;determining a reference string based on at least one of a length of thecurrent string or a string vector relating to the current string; andpredicting the current string using the determined reference string. 2.The method of claim 1, wherein the length of the current string isdetermined based on encoded string length information, and wherein theencoded string length information includes most significant bitinformation and offset information relating to the length of the currentstring.
 3. The method of claim 1, wherein determining the length of thecurrent string comprises: obtaining a string row flag relating to thecurrent string from a bitstream, the string row flag indicating whetherthe first sample and the last sample of the current string belong to thesame row; obtaining, based on the string row flag, from a bitstream,string last vector information for specifying a position of the lastsample of the current string; and determining the length of the currentstring based on the position of the first sample of the current stringand the obtained string last vector information.
 4. The method of claim1, wherein the string vector indicates a position difference between atop-left sample of a current block including the current string and atop-left sample of a reference block including the reference string, andwherein the reference string is determined to be a string at the sameposition as the current string in the reference block specified by thestring vector.
 5. An apparatus of decoding a video signal, the apparatuscomprising: a prediction unit for determining, based on a sample stringmatching technique, a length of a current string to be decoded within acurrent block, determining a reference string based on at least one ofthe length of the current string or a string vector relating to thecurrent string, and predicting the current string by using thedetermined reference string.
 6. The apparatus of claim 5, the predictionunit determines the length of the current string based on based onencoded string length information, the encoded string length informationincluding most significant bit information and offset informationrelating to the length of the current string.
 7. The apparatus of claim5, wherein the apparatus further comprises an entropy-decoding unit forobtaining a string row flag relating to the current string from abitstream, the string row flag indicating whether the first sample andthe last sample of the current string belong to the same row, andobtaining, based on the string row flag, from a bitstream, string lastvector information for specifying a position of the last sample of thecurrent string; and wherein the prediction unit determines the length ofthe current string based on the position of the first sample of thecurrent string and the obtained string last vector information.
 8. Theapparatus of claim 5, wherein the string vector indicates a positiondifference between a top-left sample of a current block including thecurrent string and a top-left sample of a reference block including thereference string, and wherein in the prediction unit, the referencestring is determined to be a string at the same position as the currentstring in the reference block specified by the string vector.
 9. Amethod of encoding a video signal, the method comprising: determining alength of a current string to be decoded in a current block, based on asample string matching technique; determining a reference string basedon at least one of a length of the current string or a string vectorrelating to the current string; and predicting the current string usingthe determined reference string.
 10. The method of claim 9, wherein thelength of the current string is determined based on string lengthinformation, and wherein the string length information is encoded withmost significant bit information and offset information relating to thelength of the current string.
 11. The method of claim 9, whereindetermining the length of the current string comprises: determiningwhether the first sample and the last sample of the current stringbelong to the same row; and encoding string last vector information forspecifying a position of the last sample of the current string when thefirst sample and the last sample of the current string belong to thesame row.
 12. The method of claim 9, wherein the string vector indicatesa position difference between a top-left sample of a current blockincluding the current string and a top-left sample of a reference blockincluding the reference string, and wherein the reference string isdetermined to be a string at the same position as the current string inthe reference block specified by the string vector.
 13. An apparatus ofencoding a video signal, the apparatus comprising: a prediction unit fordetermining, based on a sample string matching technique, a length of acurrent string to be decoded within a current block, determining areference string based on at least one of the length of the currentstring or a string vector relating to the current string, and predictingthe current string by using the determined reference string.
 14. Themethod of claim 13, wherein the prediction unit determines whether thefirst sample and the last sample of the current string belong to thesame row, and encodes string last vector information for specifying aposition of the last sample of the current string when the first sampleand the last sample of the current string belong to the same row. 15.The method of claim 13, wherein the string vector indicates a positiondifference between a top-left sample of a current block including thecurrent string and a top-left sample of a reference block including thereference string, and wherein the reference string is determined to be astring at the same position as the current string in the reference blockspecified by the string vector.